$3km + 2l - 10m + 5 = -3l - 6m + 9$ Solve for $k$.
Explanation: Combine constant terms on the right. $3km + 2l - 10m + {5} = -3l - 6m + {9}$ $3km + 2l - 10m = -3l - 6m + {4}$ Combine $m$ terms on the right. $3km + 2l - {10m} = -3l - {6m} + 4$ $3km + 2l = -3l + {4m} + 4$ Combine $l$ terms on the right. $3km + {2l} = -{3l} + 4m + 4$ $3km = -{5l} + 4m + 4$ Isolate $k$ ${3}k{m} = -5l + 4m + 4$ $k = \dfrac{ -5l + 4m + 4 }{ {3m} }$